When a vehicle trailer, such as a semi-trailer shall be disconnected from its tractor, a vertical support, which is mounted on the trailer, will be elongated down to the parking ground in order to keep the trailer in a horizontal position continuously.
At the prior art mostly telescopic supports are used, which are usually mounted in pairs at the front of the frame of a semitrailer. They nearly always consist of a hollow prop tube, out of whose interior a lower part is extended downwards for parking. Because in practice while driving, the lower part is always retracted into the interior of the prop tube, it will be briefly referred to herein as inner prop.
For moving the inner prop member in relation to the prop tube serves as a simple, cost-effective and proven drive a threaded spindle inside of the prop tube and the inner prop member. When retracting and extending the threaded spindle will be rotated via a gear, which is located on top of the prop tube.
Within the prior art conventional designs of gears and standard fastenings of support devices to a frame of the vehicle are shown in the documents EP 513 973 B1, DE 20 2004 001 054 U1 and DE 10 2006 010 831 U1.
All variants have in common that the output shaft of the gear is leading into the interior of the prop tube and is carrying there a small bevel gear, which is arranged above a corresponding, large bevel gear, which is mounted at the upper end of the threaded spindle.
The disadvantage is that the shaft with the small bevel gear and the large bevel gear need a great installation space on top of the threaded spindle, which noticeably increases the overall height of the support, even when being retracted. Due to these results: high consumption of material, high costs of material and high weight of the system.
For this type of construction the following course of the supporting force within the supporting device is typical: The supporting force is directed from the parking ground to the inner prop member and the threaded bearing, which is welded into the inner prop member, and from there via the threaded spindle in a thrust bearing inside of a pressure plate, which is welded into the outer prop tube. From there the supporting force continues in the prop tube and further via the first mounting plate at the prop tube into a second mounting plate at the vehicle frame, which is done with a frictional connection between the screw couplings of the two mounting plates. This results in the following disadvantages: Within the prop tube a strongly dimensioned pressure plate must be aligned precisely, to transmit the supporting force. The pressure plate must be welded with sufficiently dimensioned welding seam, which entails high costs of production. The crown wheel must be connected detachably to the threaded spindle. This assembly is elaborate.
Al named telescopic supports are mounted to the vehicle frame in the same manner: the prop tubes are furnished with hole perforated plates. The rows of holes and the holes have identical distances to each other. Onto the frame of the vehicle there are welded mounting plates, whose hole-patterns coincide with the perforated plates of the supports. Via these two corresponding perforated plates the supporting devices can be bolted on in that height, which is appropriate for a certain vehicle trailer.
A disadvantage is that the trailer manufacturer has to produce the mounting plates and has to attach them to the frame of the vehicle trailer. In addition, these mounting plates are welded to areas of the longitudinal girders, which are highly stressed by bending and therefore technically are notches, which can cause tension cracks especially in the bottom flanges of the longitudinal girders, when dynamic oscillations plus bending due to the load will occur.
In addition the supporting devices are generally supported backwards on the vehicle-frame.
When using two supports, which shall be driven together, holes must be drilled into the girders in the appropriate height, through which a connecting shaft is passed, which transfers the driving force between the two supports. Every support will be bolted with its perforated plate on to the mounting plate at the frame, whereby it must be guaranteed that the clamping force of all the bolted connections generate a frictional connection, which is sufficient for the maximum of the supporting force.
Another disadvantageous effort is that for the mounting of the backwardly and diagonally directed struts eyes must be welded to the longitudinal girder of the vehicles frame and must be connected with the struts.
In most cases of the practice the supports will be extracted under a high pressure of time, but without any pressure of a load. An adjustment of the height of the support under load is generally only necessary, when a second tractor must be coupled, whose semitrailer coupling is located in another height above the parking ground as that one of the first tractor, which has dropped the trailer before, and in addition the second tractor has no air spring system, with which the height of the coupling above the parking ground can be adjusted. Therefore commonly used supports are equipped with a two-speed-gearbox—one load gear and one fast gear—for driving the threaded spindle.
In these gearboxes preferentially straight-cut gear-pairs are used for the transmission. Their disadvantage is that at every pair of wheels only one pair of teeth meshes with each other. Therefore the cogwheels must be dimensioned that large that this single pair of teeth can withstand the maximum of the circumferential force. In addition gears with cogged wheels must be protected reliably from dirt. Both provisions enlarge the weight of the system.